A charged particle beam, such as an ion beam, is used to analyse and/or to process an object (sample) in a particle beam device. Such a particle beam device may comprise a charged particle source (for example, a gas field ion source) for generating ions that are used to analyse and/or to process an object.
A first charged particle source known from the prior art comprises a gas source and a gas field ion source. The gas source is able to supply one or more gases to the gas field ion source. At least one of the gases supplied by the gas source may be a noble gas (helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe)). The gas source may also supply atoms of lithium (Li), sodium (Na), potassium (K), oxygen (O), rubidium (Rb), cesium (Cs), francium (Fr), magnesium (Mg), calcium (Ca) or strontium (Sr). The gas field ion source comprises a tip with a tip apex, a first electrode in the form of an extractor electrode and a second electrode in the form of a suppressor electrode.
The tip (which may be electrically conductive) may be formed of various materials. For example, the tip may be formed of a metal. The metal may be tungsten (W), tantalum (Ta), iridium (Ir) or platinum (Pt). In other embodiments, the tip may be formed of an alloy. During use, the tip is biased positively with respect to the extractor electrode. The extractor electrode is negatively or positively biased with respect to an external ground. Moreover, the suppressor electrode is biased positively or negatively with respect to the tip. Due to the shape of the tip, an electric field is strong in the vicinity of the tip apex. The suppressor electrode assists in controlling the overall electric field between the tip and the extractor electrode. Neutral gas particles supplied by the gas source are ionized due to the electrical field and become positively charged ions in the vicinity of the tip. The positively charged ions are repelled by the positively charged tip and attracted to the extractor electrode.
A second charged particle source known from the prior art uses a trap for collecting neutral gas particles in a specific area. One embodiment of the second charged particle source comprises a single focused laser beam of a first laser to cool or trap neutral gas particles in a specific area. An alternative embodiment of the second charged particle source comprises a magneto-optical trap. A magneto-optical trap comprises an enclosure such as a vacuum chamber, a component for providing a magnetic field and a collection of first lasers. The wavelength of the laser beams of the first lasers is tuned close to, but just above, the resonance of the neutral gas particles provided by a gas source, or alternatively the laser energy is tuned just below the resonance absorption energy, thereby creating a velocity-dependent force which slows down the neutral gas particles. The magnetic field contributes position dependence to this force, creating a trap center within the overlap of the laser beams of the first lasers. A second laser, which is different from the first lasers, is used to ionize trapped neutral gas particles, to thereby form ions. The wavelength of the beam of the second laser is selected such that the energy of a photon from the second laser is just enough to ionize the trapped neutral gas particles.
US 2010/0108902 A1, US 2007/0158580 A1, US 2008/0296483 A1, US 2011/0210264 and U.S. Pat. No. 7,709,807 B2 are prior art references, which are incorporated herein by reference.
Charged particles generated by a charged particle source form the particle beam of a particle beam device having such a charged particle source. The charged particle beam current depends on the number of generated charged particles. It is obvious that a high charged particle beam current is advantageous for obtaining good imaging or processing conditions. In particular, for specific material imaging, material analysis, beam induced deposition and/or beam induced implantation, it is advantageous to have a relatively high charged particle beam current. Moreover, a relatively high charged particle beam current supports a faster scanning of a particle beam over an object at a high signal-to-noise ratio. Accordingly, there is always a need to provide a charged particle source for generating a high number of charged particles to achieve a relatively high charged particle beam current.